1. Field of the Invention
This invention relates to the manufacture of uniform glass fiber mats by the wet-laid process, and more particularly, it is concerned with improved glass fiber dispersion compositions for use in such a process.
2. Description of the Prior Art
High strength, uniform, thin sheets or mats of glass fibers are finding increasing application in the building materials industry, as for example, in asphalt roofing shingles and as backing sheets for vinyl flooring. These glass fiber mats are replacing similar sheets made traditionally of asbestos fibers. Glass fiber mats usually are made commercially by a wet-laid process, which is carried out on modified paper making machinery, as described, for example, in the book by O. A. Battista, Synthetic Fibers in Papermaking (Wiley) N.Y. 1964. A number of U.S. patents also provide a rather complete description of a wet-laid process, including U.S. Pat. Nos. 2,906,660; 3,012,929; 3,021,255; 3,050,427; 3,103,461; 3,108,891; 3,228,825; 3,634,054; 3,749,638; 3,760,458; 3,766,003; 3,838,995 and 3,905,067. The German OLS No. 2454354 (Fr. Demande No. 2,250,719), June, 1975, also is pertinent art in this field.
In general, the known wet-laid process for making glass fiber mats comprises first forming an aqueous suspension of short-length glass fibers under agitation in a mixing tank, then feeding the suspension through a moving screen on which the fibers enmesh themselves while the water is separated therefrom. However, unlike natural fibers, such as cellulose or asbestos, glass fibers do not disperse well in water. Actually, when glass fibers, which come as strands or bundles of parallel fibers, are put into water and stirred, they do not form a well-dispersed system. In fact, upon extended agitation, the fibers agglomerate as large clumps which are very difficult to redisperse.
In an attempt to overcome this inherent problem with glass fibers, it has been the practice in the industry to provide suspending aids for the glass fibers, including surfactants, in order to keep the fibers separated from one another in a relatively dispersed state. Such suspending aids usually are materials which increase the viscosity of the medium so that the fibers can suspend themselves in the medium. Some suspending aids actually are surfactants which function by reducing the surface attraction between the fibers. Unfortunately, however, none of the available suspending aids are entirely satisfactory for large volume manufacture of useful, uniform glass fiber mats.
For example, such polymeric suspending aids materials as polyacrylamides, hydroxyethyl cellulose and the like, provide a highly viscous aqueous solutions at high material concentrations, but which is difficult to handle, and particularly, which drains very slowly through the mat forming screen, or foraminous belt. Furthermore, the degree of the suspension formed using such materials is only fair, and suspensions having a fiber consistency of more than 0.005% give poor quality mats. The viscous suspensions also trap air upon agitation near the formation zone to form stable foams which adversely affect the uniformity and strength of the mats. Finally, the polymers are not effective at low concentrations, and so are expensive for use in what should be a low cost process.
A number of surfactant materials also have been tried for dispersing glass fibers in water, for example, the cationic nitrogen surfactants described in Ger. DT No. 2454354/Fr. Demande No. 2,250,719 (June, 1975). With these surfactants, the glass fiber filaments are drawn from an extruder nozzle, coated with the cationic surfactant, and moistened before chopping into short-length fibers. The chopped fibers then are compounded in another aqueous solution of a cationic surfactant. Accordingly, in this process, the cationic surfactants are applied in two stages to form an aqueous provide acceptable mats at reasonable speeds of mat production. Furthermore, the quality of the dispersions using the materials of this patent application also is poor.
Therefore, it is apparent that for a glass fiber dispersion technique to be effective, it is necessary that the dispersions meet several rigid criteria simultaneously which can provide means for making the desired high quality, uniform glass fiber mats at a rapid rate of production in an economically acceptable process. Such criteria are listed below:
1. The dispersing surfactant should provide a uniform dispersion of glass fibers in water effectively at low surfactant concentrations.
2. The dispersions should be efficient at high glass fiber consistencies so that the mats may be formed without having to expend an unnecessarily large amount of energy to separate and handle large quantities of water.
3. The dispersion compositions preferably should not be accompanied by a substantial increase in the viscosity of the medium, which would necessitate extensive pumping equipment at the screen to separate the fibers from the water, and which would make drying of the wet mat difficult.
4. The dispersion compositions should be capable of producing glass fiber mats which have a uniform distribution of fibers characterized by a multidirectional array of fibers. The finished mat product should possess uniform high-strength properties, particularly good tensile strength.
5. The dispersions should be capable of use in the wet-laid process in conventional equipment, at high rates of mat production, without generation of unwanted foams, and without corroding the plant machinery.
6. The surfactant materials preferably should be readily available, at low cost, and be capable of use either by direct addition to the fibers in water, or by precoating the fibers with the surfactant before admixing with water to form the aqueous dispersion composition.
These and other objects and features of the invention will be made apparent from the following more particular description of the invention.